Optical connector with total internal reflection abutting surface

ABSTRACT

An optical connector ( 10 ) comprises at least one optical guide ( 12 ) for carrying optical radiations; a total internal reflection surface ( 11 ) upon which, in use, said radiations impinge, so that the radiation in the optical guide is reflected by said surface towards an optical element ( 14 ) of the connector and means enabling the connector ( 10 ) to interlock with any other optical connector which is appropriately matingly configured.

FIELD OF THE INVENTION

The invention relates to optical connectors. The optical connectors inquestion may be used in a wide variety of application for exampleoptical connector arrangements for use in a fibre-optic communicationssystem, optical network sections. They may also be used for example inimproved methods to increase the functionality of an optical network.

BACKGROUND TO THE INVENTION

One of the major problems in designing optical networks is in theplacement of the optical components on the network. Design decisions onthe inclusion and placement of components need to accommodate not onlythe initial traffic on the network, but also future network growth,which is often unpredictable. This issue is especially critical forMetropolitan (or city) networks where cost needs to be minimised andgrowth is especially unpredictable.

The normal approach to the problem is to include enough elementsinitially to accommodate currently foreseen traffic growth, and to takea part of the network out of commission where additional upgrade needsto be accommodated. This is difficult to do while minimising impact onexisting traffic, and is a major operational expense. Taking part of anetwork out of commission may involve truck-rolling and splicing a newnetwork element into the existing network as and when required. Thisinvolves a heavy operational cost and can mean the network ring or linesystem is out of commission for hours at a time. A further option is toinstall an in-line connector into the network where it is thought that afuture upgrade may be required and then truck-roll and connect a newelement when it is actually needed. This also incurs a high operationalcost, though the “down time” involved is less than in the previouslymentioned case (tens of minutes instead of hours). Finally, it ispossible to install a 2×2 optical switch where the future upgrade may berequired, the switch being operated to include the new element incircuit when the need actually arises. While this is fast (<10 ms isnormally required for such switching), the reliability is lower andthere are higher losses, since two passes of the signal occur and inaddition two connectors are involved. Furthermore, most such switchesrequire a source of power and will increase the first-in cost of thenetwork.

THE PRIOR ART KNOWN TO THE APPLICANTS

Several prior art devices were identified in the following documents:

-   EP 1186932 A2-   U.S. Pat. No. 6,393,174-   U.S. Pat. No. 5,390,266-   U.S. Pat. No. 4176908

Whilst some of these disclose devices with a total internal reflectionsurface, none of these discloses the following aspects.

SUMMARY OF THE INVENTION

In its broadest aspect, the invention provides an optical connectorcomprising at least one optical guide for carrying optical radiations; atotal internal reflection surface upon which, in use, said radiationsimpinge, so that the radiation in the optical guide is reflected by saidsurface towards an optical element of the connector and means enablingthe connector to interlock with any other optical connector which isappropriately matingly configured.

This configuration is particularly advantageous because it allows theupgrading of an existing optical line with absolutely minimal disruptionto traffic. It simplifies network planning by allowing later upgradeswith optical add-drop multiplexer (OADM) filters, etc, again withminimal impact on existing traffic. It reduces capital expenditure byenabling a pay-as-you-grow policy to be followed. It decreasesoperational expenditure by simplifying the upgrading process. Itimproves network performance by eliminating unnecessary components andby allowing in-service upgrades with amplifiers and DSCM s(dispersioncompensation modules), etc.

In a subsidiary aspect in accordance with the invention's broadestaspect, the surface is such that, in use, the radiation in the opticalguide may be reflected by said surface towards an optical element of theconnector and may alternatively, in use, be such that its internalreflection properties may be frustrated to allow the radiation to passacross the surface.

In a further subsidiary aspect, the connector comprises means enablingthe connector to interlock with any other optical connector which isappropriately matingly configured and which incorporates means whichwill frustrate the total internal reflection of the first said connectorif and when the connector were to be interlocked with any such otherconnector; and with the interlock-enabling means of the connector beingso operatively positioned that, with the connector interlocked toanother suitable connector as aforesaid, the total internal reflectionsurface of the connector will be in sufficient proximity to the totalinternal reflection frustrating means of the other connector as to allowthe optical radiations to pass across the connection then formed by thetwo interlocking connectors.

In a subsidiary aspect in accordance with the invention's broadestaspect, said optical element towards which radiation is reflected insaid first mode treats the radiation so that eye-damaging radiationremains within the connector, thereby advantageously the connector mayachieve an eye-safe operation.

In a further subsidiary aspect, said connector comprises a plurality ofoptical guides. This configuration would be particularly advantageouswhen such a connector operates in a second mode with a similar matingconnector so that the connection allows radiations to be switched fromone connector port to another.

In a further subsidiary aspect, the interlocking means allow a matingconnector to be first attached in non-surface frustrating manner andthen incorporates a mechanism which provides a snap-action final closurefor the frustration of the surface.

In a further subsidiary aspect, additional reflection means are providedbetween the optical guides and the surface. This advantageousconfiguration may for example allow optical guides to be parallel withinthe connector and even normal to the total internal reflection surface.

In a further subsidiary aspect, refractive means are provided betweenthe optical guides and the surface which are adapted to change theradiation's direction as emitted from the optical guides to thedirection of the radiation incident on the total internal reflectionsurface. This may also allow optical guides to be parallel within theconnector and even normal to the total internal reflection surface.

In a further subsidiary aspect, the total internal reflection surface islocated on at least two sides of a prism. This configuration will forexample be particularly advantageous as it will allow the matingconnector to dispose at an angle (eg. 90 degrees from the connector).

The invention also provides a multiple-connector system comprising afirst optical connector in accordance with any of the preceding aspectsin combination with one or more other optical connectors, each of whichother connectors is appropriately matingly configured to interlock withsaid first optical connector in the way envisaged in the invention'sthird aspect above and with the result outlined therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a, 1 b and 1 c show three different phases in the use of anoptical connector according to the invention in a first embodimentthereof;

FIG. 2 is a diagram showing a second embodiment of a firstconnector-portion of an optical connector according to the invention;

FIG. 3 is a diagram showing the embodiment of FIG. 2 in its “mated”(second mode of use) state;

FIGS. 4 a, 4 b, 4 c and 4 d illustrate a variant version of the secondembodiment;

FIG. 5 is a diagram of a third embodiment of an optical connector inaccordance with the invention;

FIG. 6 is a diagram of a fourth embodiment of an optical connector inaccordance with the invention;

FIG. 7 is a diagram of a fifth embodiment of an optical connector inaccordance with the invention;

FIG. 8 is a diagram of a sixth embodiment of an optical connector inaccordance with the invention;

FIG. 9 is a diagram of a seventh embodiment of an optical connector inaccordance with the invention;

FIG. 10 is a diagram of the seventh embodiment in a first version of its“mated” (second mode of use) state;

FIG. 11 is a diagram of the seventh embodiment in a second version ofits “mated” (second mode of use) state;

FIG. 12 is a diagram of the seventh embodiment in a third version of its“mated” (second mode of use) state;

FIG. 13 is a diagram of the seventh embodiment in a fourth version ofits “mated” (second mode of use) state;

FIG. 14 illustrates a second optical-connector arrangement involvingmultiple optical guides;

FIG. 15 is a diagram of the first embodiment of an optical connector inits first mode of use in accordance with the invention in amoisture-resistant form;

FIG. 16 is a version of a moisture resistant connector with a seconddissimilar mating connector shown

FIG. 17 is a diagram illustrating a cascaded arrangement of opticalconnectors under the invention;

FIG. 18 shows an optical connector according to the invention in aneighth embodiment thereof;

FIGS. 19 to 21 show various applications in which the optical connectoraccording to the invention may be employed;

FIG. 22 shows a backplane implementation of an optical-connectorarrangement involving optical connectors in accordance with theinvention;

FIGS. 23 a and 23 b are diagrams showing the use of an optical connectoraccording to the invention in the first embodiment thereof as aneye-safe connector;

FIGS. 24 a and 24 b are diagrams illustrating a further embodiment of aneye-safe optical connector according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 a shows a connector comprising a body 10 which accommodates firstand second optical guides 12, 14, each of which connects at one end to arefractive element 16 by way of respective collimators 18, 20 which, inthe illustrated embodiment, is a graded-index lens (a “GRIN” lens). In afirst mode of operation, the connector may operate detached from anyother connector so that the radiation from optical guide 12 is reflectedtowards optical guide 14 via the total internal reflection surface 11 atthe glass-air interface. A protective film 13 is provided which definesan air gap 15.

The term ‘interlocking’ in this description is to be interpretedbroadly, it includes within its meaning all forms of mating attachment,contact with mutual support, intertwining and other forms of connectionother than simple connector to connector face contact.

Also included in the body 10 are interlocking means which include two ormore alignment apertures 22 for the accurate alignment (in a second modeof operation). The further connector may be selected so that when theconnectors mate the total internal reflection surface allows the opticalradiations to pass across the connection.

FIG. 1 b shows two connectors or connector portions attached to oneanother via alignment apertures.

The operation of a first connector-portion in a first mode of use of theconnector depends on the presence of an airgap (or low index medium orvacuum) at a face 24 of the refractive element 16 and, in order toprotect this refractive-element/airgap interface from fouling, aprotective cover 26 is preferably affixed thereto by some suitablemethod which will be readily apparent to the person skilled in the artof optical connector design.

In a first mode of use of the connector, in which the firstconnector-portion is separated from the second connector-portion, anoptical signal input at Port 1 of the first connector-portion willundergo total internal reflection at the glass-air interface 24 and exitfrom Port 2. Thus, where for example the first connector-portion isincluded in a network ring, the signal transmitted to Port 2 will beavailable for use elsewhere in the ring.

Assuming now that the ring is to be extended—in the manner of aretrofit—by the addition of some kind of optical element (e.g. anadd/drop multiplexer), the protective cover or film 26, where one issupplied, is removed and a second connector-portion substantiallyidentical to the first is offered up to the first connector-portion andaligned using alignment pins 28 or similar, which are inserted into theapertures 22 (see FIG. 1 b). This second connector-portion also has arefractive element, shown as element 30 in FIG. 1 b, but in this casethis element has, in a preferred realisation, an index-matching material32 coating an external face of the refractive element 30. This secondconnector-portion is offered up to the first connector-portion untilonly a very small airgap still exists between the total internalreflection surface 24 and the material (e.g. of the order of 50microns.). Then, in a process which takes much less than 10 ms (inpractice <1 ms), the second connector-portion is pushed all the waytowards the first connector-portion until the two opposing surfaces ofthe refractive elements 16, 30 are in firm contact with each other (FIG.1 c). This firm contact, assisted by the presence of the matchingmaterial, ensures that no internal reflection takes place in the firstconnector-portion and consequently the optical signal at Port 1 ispassed through into the refractive element 30 and on into the opticalguide 33 and out through Port 4. Likewise, a signal which enters thesecond connector-portion at Port 3 is passed on to the optical guide 14and out through Port 2. To ensure that optical crosstalk in the matedconnector is desirably less than −50 dB between ports 1 and 2, the indexmatching material should typically be within 0.2% of the index of therefractive element.

The mating of the two connector-portions constitutes a second mode ofuse of the connector, in which an optical element is brought into playin the network which was not present before. This introduction of a newoptical element, which is connected to Ports 3 and 4, is achieved withacceptably low loss, causes minimal interruption of traffic and can beprovisioned at very low cost, in contrast to the known conventionalmethods of extending an optical network described earlier.

A second embodiment of the optical connector according to the inventionis shown in its first mode of use in FIG. 2. In this embodiment, aferrule 60 is attached to a connector body housing 62, whichaccommodates normal items such as spring contacts, a latching mechanismand a form of strain relief. The ferrule contains first and secondoptical-signal guides, i.e. lengths of optical fibre 64, 66, which—as inthe first embodiment—feed into a collimator element 68 such as a GRINlens, the collimators leading into a refractive element 70, on two walls72 and 74 of which a reflecting means 76, 78 is provided. Thesereflecting means may take the form of a local airgap or gap filled withsome other low-index medium or a vacuum or a reflecting surface appliedto the outside of the surfaces 72, 74.

The use of these reflecting means allows the fibres 64, 66 from Port 1and Port 2 (not shown) to exit from the connector housing 62substantially parallel to one another. This has a number of advantagesin fabrication and use, due to the fact that the connector can thenemploy construction technologies which are commonly used with standardfibre-optic connectors. FIG. 3 shows two such connector-portions matedtogether in the second mode of use using a receptacle 80, which alignsthe connector-portions correctly.

A similar arrangement is shown in FIG. 4 a, but incorporating twoadditional features. The first feature is that one or both frontsurfaces of the connector-portions is polished to create a slightcurvature in the mating surfaces 83, e.g. of the order of 20 mm radius,which is common in FC/PC fibre-optic connectors. Now when theconnector-portions are mated, the closure force flattens the end of theconnector-portion(s) slightly so as to ensure a very good physicalcontact over the centre of the mating surface. Typically, the connectionforce may be around 1 kg and the glass would be flatted over an area ofaround 250 microns diameter.

The second feature is the inclusion of a snap-closure mechanism, such asa Belville™ washer 79 just in front of one of the surfaces to be mated.This is best achieved by inserting the first connector-portion ferruleinto the aligning receptacle (e.g. a bullhead connector mount 81) fromone end and then inserting the washer into the receptacle from the otherend until it touches the outer periphery of the total internalreflecting surface of the first connector-portion. Finally, the secondconnector-portion is inserted from the second end of the receptacle andpushed in until the mating surface of the second connector-portion justtouches the Belville™ washer at its outer face (see FIG. 4 b). Thecurvature in the washer automatically ensures a suitable minimum spacing(10-100 microns) between the two mating surfaces. Further pressure onthe second connector-portion forces the washer to yield and flatten and,since the washer only occupies an outer part of the total internalreflecting surface of the first connector-portion which is lessprotrusive than the inner part (see FIG. 4 c), the two mating surfacescan be brought together successfully. (There may be a more compliantspring at the back of the connector housing which can easily extend bythe 10-100 micron distance without a significant reduction in force.)

It is stressed that the Belville™ washer feature is not a requirementwhere a curved mating surface is used, but only an enhancement, allowingas it does an improved speed and control of the final closure of theconnector-portion pair.

Instead of providing a continuous curvature on one or both of the matingsurfaces, a stepped surface configuration (not shown) may be employed,whereby a flat, or even curved, mating surface gives way to a recess inwhich the washer sits, the recess of course being of such a depth thatthe washer is still able to perform its distancing function vis-à-visthe opposing mating surface.

An additional feature shown in FIG. 4 d is the incorporation of a pairof TIR (total internal reflection surfaces) interfaces internally to aconnector which is terminated in a conventional connector construction.Mechanical features embodied in this connector push the two TIR surfacestogether when this connector is mated to a conventional connector orconnector pair. This has the advantageous feature of providing a sealedvolume to protect the TIR surfaces, and the further advantageous featureof permitting interoperation with conventional connectors.

A third embodiment of the optical connector according to the inventionis illustrated in FIG. 5. This shows a curved refractive element 82 (ahemispherical ball lens), which performs the same reflective functionsas the element shown in FIGS. 2 and 3, but in addition uses its curvedsurface to perform the collimation and focussing operations.

In a fourth embodiment, shown in FIG. 6, a ferrule 86 incorporates aGraded Index (GRIN) Lens 84 employed to perform both the focussing andbeam deflection functions for radiation from fibre 85. This ispreferably a high aperture GRIN, with a numerical aperture ofapproximately 0.6, with, for example an index of 1.468 at the radiuswhere the fibre cores are attached (SMF28 fibre), thereby minimisingback reflection, and an index of 1.85 at the centre, giving a beamincidence angle of ˜35 degrees to the normal. This comfortably exceedsthe critical angle of 32 degrees between the high index material andair.

The Grin lens is ¼ of a pitch long (hence will translate position at thefibers to angle at the centre of the mating surface). With the fibres asclose together as possible, which is advantageous as it reduces theangular alignment tolerance of the connector ferrules), a typical lengthof the lens of around 0.2 mm, with a diameter at the fibre cores ofaround 125 mm, and an overall diameter of between 0.150 and 0.25 mm. Forease of handling, the length can be increased to ¾ of a pitch ifdesired. This is a particularly advantageous structure to assemble dueto the circular symmetry of the parts—the GRIN lens is a short sectionof a cylinder, the main ferrule can have a hole 3 times the fibrediameter with seven fibres in (as in FIG. 16), or their can be twofibres very close to each other in a dual hole ferrule, with thecylindrical lens attached to the end in a recess in the ferrule. Theindex range in the grin lens needed is large, and can be made by fusingconcentric tubes of different glasses together, prior to drawing down.

FIG. 7 shows a fifth embodiment incorporating a ball lens 87 with apolished planar total internal reflection surface 88 at the glass-airinterface. The lens is set to perform the deflection and collimationfunctions by refraction at the curved interface. A space 89 is providedbetween the optical guides and the ball lens which may be filled withair, a vacuum or any other appropriate low index fluid.

FIG. 8 shows a sixth embodiment incorporating an optical waveguidestructure 90 on an optical substrate 92 (e.g. silica-on-siliconwaveguides or ion-exchanged waveguides). The structure, which comprisestwo individual waveguides 94, 96, compels the optical radiation to/fromthe total internal reflection surface to meet at a point 98 on thatsurface.

A seventh embodiment of the optical connector according to the inventionis illustrated in FIG. 9, which shows a prismatic element 100 attachedto the end of a ferrule 102 accommodating the optical guides 104, 106 incombination with respective collimating means 108, 110, which again mayconsist of a GRIN lens. The prismatic element 100 provides tworeflective interfaces 112, 114 which, in the first mode of use of theconnector-portion, cause total internal reflection of the incidentoptical radiation from input to output.

FIG. 10 shows a pair of such connector-portions mated in aquasi-collinear fashion using a suitable receptacle, e.g. a bulkheadconnector mount 118. Here the optical radiation in the optical guide 104is reflected twice by the two prismatic elements and enters the opticalguide 119 to feed an optical element coupled to the secondconnector-portion, the optical radiation returned by the optical elementthen entering the optical guide 116, from where it passes from thesecond prismatic element 120 into the first prismatic element 100 andout through optical guide 106.

FIG. 11 shows an alternative version of the same arrangement where thetwo connector-portions are mated at an angle close to 90° within areceptacle 117. This arrangement can have advantages intelecommunications equipment, since it reduces the space needed toaccommodate fibre-bend radii by providing a “corner reflector” function.The optical-signal paths are as shown by the arrows.

FIG. 12 shows yet another alternative version of the same arrangement,but this time exploits the fact that there are two reflecting surfacesin the prismatic element employed, such that two independentconnector-portions 132, 134 can be mated with the firstconnector-portion 130. This arrangement has the advantage that, althoughit provides the function of two connectors, the through-loss in theunconnected state (first mode of use) of the first connector-portion 130is that of a single connector only. The optical-signal paths are againshown by the arrows.

A further arrangement is envisaged within the scope of the inventionwith four such connector portions operating conjointly.

FIG. 13 shows an optical-connector arrangement, in which aconnector-portion contains a number of pairs of optical guides (fibres)arranged in parallel or in any other direction as appropriate, thenumber shown being three pairs with one central fibre. Due to thesymmetry of the structure, it is possible to arrange the seven fibresshown along the centre of the ferrule with a high degree of accuracy. Inthe example shown fibre 1 is paired with fibre 2, fibre 3 is paired withfibre 4, and fibre 5 is paired with fibre 6. The central fibre 7operates as a standard “straight through” connector, which could beuseful in monitoring closure of the connector. This arrangement has thebenefit that multiple connections can be simultaneously made by sharingthe same mating aperture. It should be apparent that a different numberof pairs of fibres may be similarly arranged by changing the diameter ofthe centre fibre and, further, this feature can be used in combinationwith any of appropriate beam collimation and redirection methods.

FIG. 14 shows an alternative multi-fibre arrangement. In thisarrangement, two arrays of fibres are aligned vertically one aboveanother, and pairs of fibres are associated with respectiveconnector-portions. There are shown four connector portions 141 with aconnector alignment groove 142. Preferably, this is constructed by usingtwo arrays of fibres mounted in alignment grooves in a substrate such assilicon or plastic, the two arrays then being vertically alignedrelative to each other in order to achieve fibre pairings. An array ofoptical elements used for the reflection and focussing functions may beformed using any of the optical devices shown in any appropriatepreceding figures.

Advantageously, in such multi-fibre connector arrangements, the actionof mating connectors will disconnect some pairs of fibres, whilesimultaneously mating other pairs of fibres. This will have a number ofnetwork applications.

In order to eliminate or at least minimise moisture ingress orcondensation, the invention envisages the use of a moisture-tight cap onthe end of the first connector-portion, thereby retaining the air gap,or the provision of a single-use sacrificial protective layer, as shownin FIG. 1 a. However, this approach may be deemed unreliable in someapplications, and it does not permit the end-face (mating surface) ofthe connector-portion to be cleaned without disrupting the totalinternal reflection. In addition, once the protective layer or end-capis removed, condensation may form on the end of the connector,disrupting the total internal reflection, and thus increasing the lossof the connector and destroying the inherent eye-safe property of theconnector (see later).

A moisture-resistant first connector-portion is shown in FIG. 15. Thisincorporates a thin block of glass 151 of substantially the same indexas the prism shown, retained by a flexible membrane 152 which holds it afew microns offset from the prism surface 153, and which also acts as ahermetic seal. A void 154 is formed between the glass block and theprism surface which is hermetically or moisture sealed. When two suchconnectors are mated, the flexible membrane is deformed allowing boththin glass blocks to contact the prisms, thus allowing the opticalsignals to pass through to the opposing optical guides. This connectortherefore has the advantage of being moisture-resistant, and alsopermitting easy cleaning without disrupting the total internalreflection when in the unmated state.

FIG. 16 shows a preferred embodiment of a moisture-resistant opticalconnector. The first connector-portion on the left ismoisture-resistant. It has a thin membrane 161 of index-matched glass(e.g. 20 microns thick) spaced from the total internal reflectionsurface 162 by glass blocks 163 of for example, 10 microns andhermetically enclosing a compressible, non-condensing, low-index medium165 such as dry nitrogen. The right-hand connector-portion is notmoisture-resistant, and has a curved surface 164 of, for example, 10 mmradius. When these two connector-portions are closed, the roundedsurface of the second connector-portion forces the glass membraneagainst the surface 162, thereby coupling the optical signal to ports 3and 4.

To minimise levels of cross coupling in the mated state, the matingsurface of the glass block membrane can be at a small angle to theinternal TIR surface. Alternatively or in addition, cross coupling andloss in the mated state may be reduced by the addition of a small amountof index-matched fluid to the mating surface prior to connection.

An alternative design of moisture-resistant connector is to select therefractive index of the first connector-portion end-face to be such thattotal internal reflection will still occur even when this end-face iscoated with moisture. An example of a suitable material for this purposeis TiO₂ (rutile), having a refractive index of around 2.2. It should benoted that, where materials of dissimilar refractive indices are used,antireflection coatings may be employed to reduce losses where required.

Multi-Path Interference (MPI) can occur when an optical signal can besplit into two paths and then recombined. In a number of applications,MPI needs to be kept very low—example, the interfering signal needs tobe 50 dB lower in magnitude than the main signal. When the connectoraccording to the invention couples in an optical element, as in FIG. 1,residual reflectivity within the connector in the mated state canconstitute an interfering signal.

FIG. 17 shows a method of cascading two connectors to double the MPIrejection. In the unmated state the signal takes the path Port 1-Port2-Port 1A-Port 2A, undergoing total internal reflection twice. Thenetwork element 160 is connected from Port 4 to Port 3A. In the matedcase, the main path is Port 1-Port 4-network element-Port 3A-Port 2A,while the Interfering signal takes the path Port 1-Port 2-Port 1A-Port2A. In this case, the unwanted signal undergoes two reflections(example, −40 dB each, giving total rejection of −80 dB). The twoconnectors are preferably part of a multi-way connector structure, as inFIG. 13 or FIG. 14. Alternatively, Port 2 could be connected internallyto Port 1A, for example using an internal reflector.

A final embodiment of the optical connector in accordance with theinvention is illustrated in FIG. 18. In FIG. 18 an optical connector inits second mode of use comprises first and second connector-portions400, 402, in which are accommodated optical guides 404, 406, 408, 410without the addition of collimators or refractive elements. These guidesconverge at an angle (e.g. 45°) onto the respective mating surfaces,where again the mating surface of the first connector-portion 400 actsas a total internal reflector in the first mode of operation. Since thetwo connector-portions are in contact with each other, the opticalradiation in the optical guide 404 is passed straight through to theoptical guide 408 and the return radiation entering the guide 410 ispassed straight through to the guide 406.

In this embodiment, it is important that the mating ends of the opticalguides be accurately cut and polished so as to avoid spurious airgaps,which might impair the transmission from the first connector-portion tothe second and vice-versa.

It is worth mentioning that, for certain functions, the new opticalelement need not be external to the second connector-portion, but couldbe integral with it. Examples would include filters, taps, sensors,isolators and/or optoelectronic components.

FIG. 19 shows a particular advantageous use of the inventive connector.A first connector-portion (or connector) 170 is included into a line, asshown. An optical add drop multiplexer (OADM) filter 174 is connected toa second connector-portion in a loop configuration. When the two halvesof the connector are mated, the signal is rerouted through the OADMfilter. The interruption to the traffic is brief (<<10 ms), which can betolerated by many optical systems. In order to include further expansioncapability, a second optical connector according to the invention 176can be included in the loop.

The connector may also be used to provide flexibility points betweenamplifier nodes.

In a number of upgrade or maintenance scenarios, it is useful to be ableto measure an optical signal on the line without breaking the trafficpath. This can be accomplished by means of a connector coupled to a tapcoupler 200 (which typically taps 1% to 10% of the signal), as shown inFIG. 20. Again, the connector breaks the optical path for <<10 ms. Thetapped signal can then be fed to measurement equipment 202 as required.

An alternative means of introducing an optical tap is by creating asmall separation of order 1 micron between the two mating surfaces ofthe connector, which would cause partial frustration of the reflectionat the interface and thereby allowing a fraction of the light in thefirst connector-portion to be coupled in to the respective guides of thesecond connector portion. One way in which this separation could beachieved is by appropriate design of the snap-action mechanism describedearlier such that an intermediate closure force brings the two surfacesto a defined spacing.

Using the connector, an amplifier 204 may be inserted into a line.

FIG. 21 shows the use of a connector in accordance with the invention tolink two existing rings—a main ring 206 and a secondary ring 208—into asingle larger ring. In practice, to achieve this the following steps arepreferably taken: firstly, before the two connector-halves are mated,the traffic at those ring nodes adjacent the first connector-portion isrerouted; then the connector halves are mated and new paths arecommissioned through the enlarged ring and, finally, the new paths aremade available to the traffic which had been rerouted.

Dispersion is an important problem in many optical systems, since itcauses pulse spreading as the signal travels along fibre systems.Dispersion is a particular issue on higher speed systems (10 Gbps andupwards) or with non-optimum fibre types. A simple optical-fibre system(e.g. 2.5 Gbps, few wavelengths) can be deployed with minimal dispersioncompensation. Upgrade of some wavelengths to 10 Gbps/40 Gbps thenrequires the addition of Dispersion Compensating Modules (DCMs) orDispersion Slope Compensating Modules (DSCMs). This can be accomplishedby first measuring the signal quality using an optical connectoraccording to the invention with tap coupler and dispersion measurementequipment, as partially described in connection with FIG. 20. Thedispersion measurement equipment can then be used to calculate theoptimum value of a fixed dispersion compensation. This tap coupler andmeasurement equipment can then be replaced by a low-cost fixed DCM orDSCM.

FIG. 22 shows a number of connectors 220 a, 220 b in accordance with theinvention being used in an optical backplane application. Theconfiguration allows circuit boards 222 to be plugged into the backplane224, with the optical signal being routed through each such board to anoptical element or module 226 mounted on the board. The backplaneconnectors may be single connectors or “multiple” connectors. Variousconfigurations of “wiring up” the backplane are of course possible, onlyone being shown here. It is advantageous in this application to useconnectors which permit the signal to be rotated through large angles,for example as shown in FIG. 11. A mix of connector types is of coursepossible, e.g. a connector-portion configuration as shown in FIG. 1 onthe backplane together with a mating connector-portion configuration asshown in FIG. 2. This requires that the optical radiations (beams) inthe optical guides subtend the same angles in the two configurations(e.g. 45° to the normal) and that the beam diameters and index of themating surfaces also match between the two. The external interface tothe backplane (if required) may be directly via an off-shelf connector228, or could be via on-card connectors (not shown).

The first connector-portion of an optical connector according to theinvention will not emit significant levels of radiation when employed inits first mode of use, provided the second optical guide is properlyterminated. Where the optical connector is only required to be of thesingle-port type, it is possible to terminate the second port (secondoptical guide) internally within the connector. FIG. 23 a shows thefirst connector-portion of the afore-described first embodiment of anoptical connector according to the invention, in which a fibre 300 isaccommodated in the body 302 of the connector portion and communicateswith a collimating element 304, which in turn is connected to a prism306 acting at its outwardly facing side 310 as a total internalreflecting surface. A protective cover 308 may optionally also beprovided as explained earlier.

Different here, however, is the fact that the optical signal reflectedfrom the surface 310 is absorbed in an optical dump 312 provided on theface 313 of the prism 306 upon which the reflected signal impinges. Asan alternative, a reflector may be provided at this point, which willreflect the impinging signal back along substantially the same path,this return signal then being again reflected from the face 310 and backalong the optical fibre 300 in the opposite direction. This will havethe effect of enhancing the return signal which is relied on in theearlier described ALS systems. (In such known systems the mainreflecting surface (here 310) is usually normal to the fibre axis). Ifit is desired to maintain the same reflectivity as a standard FC/PC typeoptical connector, the reflector could be in the form of an air gap.

The more normal mode of operation of such an eye-safe arrangement is tohave the first connector-portion illustrated in FIG. 23 a connected toits corresponding second connector-portion (see FIG. 23 b). The latterwould take the form of the second connector-portion shown in FIG. 1 b.As with the first connector-portion shown in FIG. 23 a, this secondconnector-portion would have a single optical port (optical guide) forpassing the optical signal on to the fibre section to which the secondconnector-portion was connected.

As a still further alternative, a fluorescent material may be used asthe coating 312, this then providing a visual indication of the presenceof an optical signal within the connector to service personnel, who canthen take any required action.

A variant of the latter arrangement would be to provide means forvisually indication a fibre break. This may be achieved by replacing theafore-mentioned coating 312 by a string of three or four photodiodes inseries with a visible LED or laser 314.

Of course, instead of using the angled optical-guide configuration ofthe first embodiment (FIG. 1), any of the other configurations may alsobe employed as appropriately selected by the person skilled in the art.

A second embodiment of an eye-safe connector arrangement is the subjectof FIGS. 24 a and 24 b, in which a fibre is shown terminated in aconnector-portion 320. The end of the fibre, which is received in areceiving means 321 is inserted in a ferrule 322 which may be 2.5 mm indiameter, the outer end of which may be polished off 1.5 mm at an anglegreater than 50 degrees to the angle of the core, as shown. The cut, anenlarged version of which is shown as item 324 in FIG. 24 b, is made sothat the optical signal impinging on the angled end-face of the ferruleis reflected towards the side-wall of the ferrule, as shown by thearrow, where it is absorbed.

In the other mode of use of the illustrated connector, a similarconnector-portion is offered up to the end of the ferrule of theconnector-portion 320 shown, so that the total internal reflectingoperation at the ferrule/air interface 324 is frustrated, the signalthen being able to pass into the opposing ferrule 325 and out into itsown associated fibre section

1. A first optical connector comprising: at least one optical guide forcarrying optical radiations; a total internal reflection surface upon atleast a portion of which, in use, said radiations impinge, so that theradiation in the optical guide is reflected by said surface towards anoptical element of the first connector; and a push-fit portion forattaching and aligning said first optical connector to a second opticalconnector which is appropriately matingly configured, said portion ofsaid total internal reflection surface being disposed independent ofsaid push-fit portion.
 2. A first optical connector according to claim1, wherein the surface is such that, in use, the radiation in theoptical guide may be reflected by said surface towards an opticalelement of the connector and may alternatively, in use, be such that itsinternal reflection properties may be frustrated to allow the radiationto pass across the surface.
 3. A first optical connector according toclaim 1 further comprising wherein the second connector incorporatesmeans which will frustrate the total internal reflection of the firstconnector if and when the first connector were to be interlocked withthe second connector; and with the push-fit portion being so operativelypositioned that, with the first connector interlocked to the secondconnector as aforesaid, the total internal reflection surface of thefirst connector will be in sufficient proximity to the total internalreflection frustrating means of the second connector as to allow theoptical radiations to pass across the connection then formed by the twointerlocking connectors.
 4. A first optical connector according to claim1, wherein said optical element towards which radiation is reflectedtreats the radiation so that eye-damaging radiation remains within thefirst connector.
 5. A first optical connector according to claim 1,wherein said first connector comprises a plurality of optical guides. 6.A first optical connector according to claim 1, wherein said push-fitportion incorporates interlocking means allowing a connector to be firstattached in a non-surface frustrating manner and then incorporates amechanism which provides a snap-action final closure for the frustrationof the surface.
 7. A first optical connector according to claim 5further comprising additional reflection means between the opticalguides and the surface.
 8. A first optical connector according to claim5 further comprising refractive means between the optical guides and thesurface which change the radiation's direction as emitted from theoptical guides to the direction of the radiation incident on the totalinternal reflection surface.
 9. A first optical connector according toclaim 5, wherein the total internal reflection surface is located on atleast two sides of a prism.
 10. A first optical connector according toclaim 1, wherein the push-fit portion comprises at least one alignmentpin.
 11. A multiple-connector system comprising: a first opticalconnector including, at least one optical guide for carrying opticalradiations, a total internal reflection surface upon at least a portionof which, in use, said radiations impinge, so that the radiation in theoptical guide is reflected by said surface towards an optical element ofthe first connector, a push-fit portion for attaching and aligning saidfirst optical connector to another optical connector which isappropriately matingly configured, said portion of said total internalreflection surface being disposed independent of said push-fit portion;and one or more other optical connectors, each of which other connectorsis appropriately matingly configured to attach to and align with saidfirst optical connector and which incorporates means which willfrustrate the total internal reflection of said first connector if andwhen the other connector were to be fully pushed against said firstconnector, wherein the push-fit portion of said first connector isoperatively positioned so that with said first connector fully pushedagainst said other connector as aforesaid, the total internal reflectionsurface of said first connector will be in sufficient proximity to thetotal internal reflection frustrating means of said other connector asto allow the optical radiations to pass across the connection thenformed by the two attached connectors.